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Full text of "Text Book Of Mechanical Engineering"

14

Loam Patterns.

Loam Moulding.óWe shall now proceed to consider the
moulding of such objects as may be done wholly or partly in
loam by striking (or strickling), and first we will take an ordinary
Gas Pipe Main, with spigot and faucet, the former being the
smaller end of the pipe, which fits loosely into the faucet or larger
end of the next pipe, see Fig. 22, which represents the finished
pipe in section. To mould the outer envelope, we may either

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have a wooden pattern with the core prints at the ends, or may
strike out a loam pattern from a board. Assuming the latter
method, we need first a pair of trestles, Fig. 23, on which is
placed a hollow cast iron cylinder with journals at the ends, and
pierced with holes along its length for the venting of the core.

Round this cylinder straw rope is tightly coiled, after which a
layer of loam is laid on. The loam being dry, a second coating
is applied, and this time, as the handle is turned, the shape of
the core is struck out by means of a board B secured to the trestles.
The core b being dried in the stove, is blackwashed, and then
covered with another layer of loam to be struck out by the second
board A, and so the loam pattern is formed. Being again dried,
an impression is made in the mould, after which, the last applied
loam, or thickness piece, is removed, the blackwasb facilitating this,
and the internal core b being returned to its proper place in the
mould (see Fig. 24), gate is made, and casting performed as usual.

It is advisable to cast these pipes either vertically, or on an
incline, so that the metal may flow more easily and bring the
scum to. the end, and if they are very long, dry sand should be
used in the boxes instead of green sand, for reasons previously
stated. After the metal is poured, the escaping gas is lit at
either end of the pipe. (See Appendix //, p. 782.)

Fig. 25 represents the moulding of a Bend for the pipe in last